Methods of and apparatus for dissolving surface projections, electropolishing and passivating metallic tapes



Nov. 29, 1955 H. R. STROBEL 2,725,352

METHODS OF AND APPARATUS FOR DISSOLVING SURFACE PROJECTIONS, ELECTROPOLISHING AND PASSIVATING METALLIC TAPES Filed July 21, 1950 2 Sheets-Sheet l o l: w m a: 3 3: I: I

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INVENTOR HRST BEL ATTORNEY Nov. 29, 1955 H. R. STROBEL 2,725,352

METHODS OF AND APPARATUS FOR DISSOLVING SURFACE PROJECTIONS, ELECTROPOLISHING AND PASSIVATING METALLIC TAPES 2 Sheets-Sheet 2 Filed July 21, 1950 FIG. 3

ATTORNEY United States Patent METHODS OF AND APPARATUS FOR DISSOLVING,

SURFACE PROJECTIONS, ELECTROPOLISHING AND PASSIVATING METALLIC TAPES Application July 21, 1950, Serial No. 175,125 I 7 Claims. (Cl. 204-28) This invention relates to methods of and apparatus for electropolishing metallic articles, and more particularly to methods of and apparatus for electropolishing metallic filaments, such as tapes, wires, and the like.

In the manufacture of coaxial cable units of the type in which an outer tubular conductor made from a metallic tape is supported concentrically on a central, wire-like conductor by insulating discs or the like, it is important that the inner surface of the tape andthe surface of the central conductor used in making such a unit be free of ridges, splinters, bumps and other types of projections in order for the electrical characteristics of the unit to be uniform throughout the length of the unit. In the past, this result has been diflicult to achieve. Other industries also require metallic elements having smooth, polished surfaces.

An object of the invention is to provide new and improved methods of and apparatus for electropolishing metallic articles. 7

A further object of the invention is to provide new and improved methods of and apparatus for electropolishing metallic filaments such as tapes, wires, and the like.

Another object of the invention is to provide new and improved methods of and apparatus for removing splinters, metallic flakes, ridges and other projections from copper tapes used in making coaxial cable units. A

A method illustrating certain features of the invention may include advancing a metallic article as an anode through an electrolytic bath having a cathode therein,

impressing a difference of potential across the article and the cathode to create a current density on the article sufficient to dissolve projections on the surface thereof but insufiicient to passivate its surface, and gradually moving the article closer to the cathode to increase the current density thereon sufficiently to passivate said surface thereby controlling the dissolving action. I I

An apparatus illustrating certain features of the inven tion may include an electrolytic bath, means for immersing a metallic article in the bath, means for advancing the article through the bath along a predetermined path, an electrode immersed in the bath, means for creating initially a current density on the article suflicient to erode away projections from the surface of the article but insufiicient to cause rapid passivation of the article, and means for causing subsequently a current density on the article suificient to cause rapid passivation of the article.

A complete understanding of the invention may be obtained from the following detaileddescription of a method and an apparatus forming specific embodimentsthereof, when read in conjunction with the'appended drawings, in which:

Fig. 1 is a fragmentary side elevation of a portion of an apparatus for effecting one method. embodying the invention;

Fig. 2 is a fragmentary side elevation of another portion of the apparatus continuedfrom the right hand end ofFig. 1; t

Patented Nov. 2%, 1955 Fig. 3 is an enlarged, top plan view of a portion of the apparatus shown in Fig. 1;

Fig. 4 is an enlarged vertical section taken along line 44 of Fig. 3, and

Fig. 5 is a view of a portion of one type of tape which may be treated by methods and apparatus embodying the invention.

Referring now in detail to the drawings, there is shown therein an electropolishing apparatus, which serves to electropolish one face of a copper tape 10 having serrated edges 11.-11. The tape 10 is advanced continuously by rolls 8-8 through a suitable alkaline cleaning bath 12,

'a water rinsing bath 14, an electropolishing bath 18, a

water rinsing bath 20, an alkaline neutralizing bath 22 and a water rinsing bath 24. The tape 10 is drawn from a supply stand (not shown) and is wound on a takeup device 25.

The bath 18 preferably is an electrolyte having a composition the same as that of, and held in the temperature ranges of, the electropolishing electrolyte disclosed in my copending application Serial No. 175,124, filed July 21, 1950, for Electropolishing Metallic Articles. The electrolyte may consist essentially of about 18% to 30% by weight copper nitrate, 6% to 2% by weight sulphuric acid and 76% to 68% by weight water, and the temperature of the electrolyte preferably is from 65 F. to 110 F. One very successful electrolyte consisted of 19% copper nitrate, 4.5% sulphuric acid and 76.5% water, and was maintained at a temperature of from about F. to F. If desired a suitable water soluble wetting agent, such as, for example, a sodium salt of an alkyl naphthalene sulphonic acid, or an ester of a sulphonated bicarboxylic acid, which are commonly sold under the trade name Aerosol, may be used in the electrolyte.

A contact sheave 34 (Fig. 1) contacts the tape 1% at a point prior to the entrance of the tape into the bath 18, and is connected to the positive side of a source of D. C. potential (not shown), the negative side of which is connected to a contact roll 40. A driven roll 42 advances a cathode tape 44 through the bath 18 in the same general direction as that in which the tape 10 is advanced therethrough, and contact sheaves 45-45 guide the cathode tape 44 in a direction converging with respect to the tape 10 from the entrance end of the electropolishing bath 18 tothe exit end thereof. As the tape 10 passes through the bath 18, the voltage between the cathode tape 44 and the tape 10, the spacing between the two tapes and the conductivity of the bath are such that any projections on the surface of the tape 10 are first dissolved therefrom by electrolytic action under an anode current density that is high but below 3,000 amperes per square foot. This anode current density is increased as the tape approaches the exit end of the bath to over 3,000 amperes per square foot to form a' layer of copper oxides on the face of the tape 10 nearer the cathode tape 44 to polish and passivate that face by the time the tape 10 leaves the bath 18.

The bath 18 is contained in a tank 52 supported by a frame 53. A pair of spaced apertures 54-54 are provided at the entrance end of the tank 52 for the passage therethrough of the tapes 10 and 4-4. The distance between these tapes gradually decreases as they approach the exit end of the tank and emerge through a single aperture 55.

A mask 50 composed of a nonconductive material such as wood or plastic having agroove 51 therein extends along the bath 18, and covers the back of the tape 10 and brackets 56-5 56 Operation The tape 14) is advanced continuously through the baths l2, l4, l8, Ztl, 22 and 24. The bath 1?; cleans grease and other foreign matter from the tape 1% and the water rinsing bath l4 rinses the alkali from the tape. he cathode tape 44 is advanced along the tape it) at the same rate of speed as that of the tape 10. During the initial portion of the passage of the tape lfi through the bath 1%, the resistance between the two tapes is sufficiently high to prevent rapid passivation of the front face of the tape 10, and is sufiiciently low to cause all larger projections on the front face of the tape iii to be dissolved electrolytically.

The current density on the front face of the tape 1d increases asthe tape Ill moves from the entrance end of the bath 18 toward the exit end thereof because of the continuous shortening of the path between the tape it and the cathode tape- As the current density increases, the portion of the electrolyte immediately adjacent to the front face of the tape is broken down to provide oxygen, which reacts with the copper coming from the tape to form copper oxides on the front face of the tape 10. This face of the tape ltl below the copper oxides is polished highly by the time the oxides build up to a passivating condition. Slightly before the tape leaves the bath 18, this passivating condition is reached which reduces current flow to a small value. Thus, the passivation acts as a control to stop substantially further dissolution of copper from the tape.

After passivation, the front surface of the tape has a lustrous, light green coating thereon composed of copper oxides. This oxide layer is removed from the conductor by the alkaline bath 22, which dissolves it and leaves a smooth golden surface on the front face of the tape.

The movement of the tape it! through the electropolishing bath 13 is sufficiently slow to prevent agitation around the front face of the portion of the tape in the bath 18. As a result, the breakdown of electrolyte produced along the front face of the tape by the electrolytic action is such that there is sufficient supply of oxygen available at the front face of the tape to form the copper oxides. The copper oxides passivate the front face of the tape to limit polishing of this surface when it has become smooth.

In one example, each portion of the front face of the tape 10, which was 1 /8 inches wide, was subjected to electrolytic polishing in the bath 18 for a periodv of from 10 to 15 seconds, and the bath 18 was about four feet long. The cathode tape 44 also was about 1% inches wide. The portions of the tapes 16 and. 44 entering the bath 1% were about 1 /2 inches apart, and the portions of the tapes leaving the bath were spaced inch apart. The voltage between the tapes in the bath was 18 volts. The composition of the electrolyte in the bath 18 was 19% copper nitrate, 4.5% sulphuric acid and 76.5% water, and the electrolyte was maintained at a temperature of from about 80 F. to about 85 F. The average current density on the face of the tape 10 being polished was about 1,600 amperes per square foot.

The above-described method rapidly forms lustrous, highly polished surfaces on articlesoriginally having projections on the surfaces thereof, and the polished surfaces have no pits therein.

Certain features of the above-described bath and method are disclosed and claimed in my above-mentioned application Serial No. 175,124. Other features of the method and certain features of the apparatus are described and claimed in copending application Serial No. 175,189, filed July 21, 1950, by- A. N. Gray for Methods of and Apparatus for Electropolishing Metallic Articles.

In the use of terms filament and filamentary article in the specification and claims it is intended to include rods, wires, tapes, bands, and the like.

Articles composed of metals other thancopper may be successfully polished with the above-described method and apparatus in conjunction with a suitable electrolyte. For example, articles made of steel, stainless steel, zinc, brass, nickel, etc. may be successfully polished with methods and apparatus embodying the invention. Furthermore, such methods and apparatus successfully electropolish composite articles having an outer covering of one metal enclosing an innercore of another metal. One particular material that may be thus electropolished is a composite wire composed of a steelcore incased in a copper sheath.

What is claimed is:

l. The method of. dissolving. surface projections, electropolishing and passivating metallic tapes having serrated edges, which comprises advancingv a filamentary cathode longitudinally along a predetermined path through an electrolytic bath, advancing, such ametallic tape longitudinally through the bath along a path which progressively approaches the path of the cathode from the entrance end to the exit end-of'the bath, masking the edges of the tape with electrical insulating material to prevent electrolytic action on' the serrated portions thereof, and creating a substantially constant potential difference between the cathode and the tape to electropolish the surface of the tape in the initial portion of the bath and ultimately topassivate said surface near the exit end of the bath.

2. The method of dissolving surface projections, elec- V tropolishing and passivating filamentary metallic articles,

which comprises'advancing a metallic filament longitudinally as an anode along apredetermined path through an electrolytic bath, advancing a filamentary cathode through the bath at the same speed and in the same generaldirection as the filament in a path which gradually converges upon the path of the filament, thereby gradually decreasing the distance between the cathode and the filament as they advance from the entrance end to the exit end of the bath, and impressing a substantially constant difference of potential between the filament and the cathode sothat the current. density on the surface of the filament most adjacent to the cathode is sufiicient to dissolve nodes on said surface in the initial portion of the bathbuttoo low to cause passivation thereof and the current density thereon gradually increases until rapid passivation of said surface occurs near the exit end of the bath.

3. The method of dissolving surface projections, electropolishing and passivating filamentary metallic articles, which comprises advancing a metallic filament longitudinallyin a substantially straight path through an electrolytic bath, advancing a filamentarycathode through the bath at the same speed and inthe same general direction as the filament in a substantially straight path converging upon the path of the filament so that they are closest near the exit end of the bath, and creating a substantially constant difference of potential across the filament and the cathode such that the'current density on the filament as it enters thebath is about 1600 amperes per square foot and progressively increases to' about 3000 amperes per square foot at the exit end of the bath, whereby nodes and projections on the surface of the filament are dissolved away in the initial portion of the bath and subsequently the surface becomes passivated.

4. An apparatus for electropolishing metallic filaments, which comprises an electrolytic cell for holding an electrolyticbath and having an entrance. end. and an exit end, means for introducing a. metallic filament into the cell near'the entrance end thereof for immersion in an electrolytic bath therein, means for advancing the filament longitudinally through the cell along a predetermined straight path to the exitend'the'reof, a cathode extending through the cell in a straight path in the same general direction as and converging with respect to the path of the filament throughout the active portion of the cell, and.

means forcreating a difference of potential between the filament and the cathode.

5. An apparatus for electropolishing metallic filaments, which comprises an electrolytic cell for holding an electrolytic bath and having an entrance end and an exit end, means for advancing a metallic filament longitudinally at a predetermined speed in a substantially straight path through the cell from the entrance end to the exit end thereof, means for advancing a filamentary cathode through the cell at the same speed and in the same general direction as the filament in a substantially straight path which converges upon the path of the filament throughout substantially the entire length of the cell, and means for impressing a difference of potential across the filament and the cathode.

6. An apparatus for electropolishing metallic filaments, which comprises an electrolytic cell for holding an electrolytic bath and having an entrance end and an exit end, means for continuously advancing a metallic filament longitudinally at a predetermined speed in a substantially straight path through the cell from the entrance end to the exit end thereof for submersion in an electrolytic bath in the cell, an endless cathodic tape movable in a path having a substantially straight portion adjacent to the path of the filament from near the entrance end to near the exit end of the cell, the substantially straight portions of the paths of the filament and the cathodic tape converging gradually so that the tape and the filament constantly approach each other throughout the active portion of the cell, means for advancing the cathodic tape at the same speed at which the filament is advanced, and means for impressing a difierence of potential across the filament and the cathodic tape.

7. An electropclishing apparatus, which comprises an electrolytic bath having an entrance end and an exit end, a mask composed of electrical insulating material extending substantially from the entrance end of the bath to the exit end thereof and having a groove extending therealong, means for advancing a tape through the groove in the mask whereby one face and the edges of the tape are covered by the mask, means for advancing a filamentary cathode through the bath along a substantially straight path adjacent to and spaced from the groove in the mask and gradually converging with respect to the groove in the mask from the entrance end of the bath to the exit end of the bath, and means for impressing a difference of potential across the tape and the cathode, whereby the exposed portion of the tape is subjected to a gradually increasing current density from the entrance end of the bath to the exit end of the bath.

References Cited in the file of this patent UNITED STATES PATENTS 2,023,998 Fustier Dec. 10, 1935 2,115,005 Blaut et al. Apr. 26, 1938 2,304,577 Leguillon Dec. 8, 1942 2,378,002 Drummond et al June 12, 1945 2,428,141 Burkhardt Sept. 30, 1947 2,479,302 Bondley Aug. 16, 1949 FOREIGN PATENTS 119,031 Austria Sept. 25, 1930 587,445 Germany Nov. 3, 1933 

1. THE METHOD OF DISSOLVING SURFACE PROJECTIONS, ELECTROPOLISHING AND PASSIVATING METALLIC TAPES HAVING SERRATED EDGES, WHICH COMPRISES ADVANCING A FILAMENTARY CATHODE LONGITUDINALLY ALONG A PREDETERMINED PATH THROUGH AN ELECTROLYTIC BATH, ADVANCING SUCH A METALLIC TAPE LONGITUDINALLY THROUGH THE BATH ALONG A PATH WHICH PROGRESSIVELY APPRAOCHES THE PATH OF THE CATHODE FROM THE ENTRANCE END TO THE EXIT END OF THE BATH, MASKING THE EDGES OF THE TAPE WITH ELECTRICAL INSULATING MATERIAL TO PREVENT ELECTROLYTIC ACTION ON THE SERRATED PORTIONS THEREOF, AND 